1. Field of the Invention
This invention relates, generally, to improvements in chain saws. More particularly, it relates to an improvement that enables the chain of a chain saw to be loosened or tightened without requiring loosening of locking nuts that secure a chain-carrying blade of the saw to the motor housing of the saw.
2. Description of the Prior Art
Chain saws include an elongate flat blade having a peripheral edge about which a cutting element, also known as a chain, extends in a continuous, endless loop. The distal free end of the chain is used for cutting. The proximal end of the chain extends around a sprocket gear that engages the chain and causes it to rotate around the peripheral edge of the elongate flat blade when the sprocket gear is rotated. The sprocket gear is attached to the output shaft of a motor means that is housed in a motor housing, and the proximal end of the elongate flat blade is secured to the motor housing.
More specifically, an elongate slot is formed in the proximal end of the elongate flat blade, and a pair of externally threaded post members that are secured to the motor housing respectively extend through the apertures. Each post member has an unthreaded base having a diameter greater than the diameter of the threaded part of the post, and the respective bases are recessed with respect to the elongate slot formed in the elongate flat blade. A pair of internally threaded locking nuts respectively screw threadedly engage the threaded part of the post members and securely lock the elongate flat blade against movement when the nuts are tightly seated. The nuts do not contact the respective base members of the posts due to their recessed position.
A worm gear means is employed as a part of a blade position adjustment means that displaces the elongate flat blade in a first direction to loosen the chain and in a second, opposite direction to tighten the chain. However, when the elongate flat blade is tightly secured against movement by the locking nuts, the blade position adjustment means cannot perform its function because the elongate flat blade cannot be displaced when said locking nuts are firmly seated.
Accordingly, to tighten or loosen the chain, both locking nuts must be loosened. After a tool such as a screw driver is used to manipulate the blade position adjustment means until the chain is loosened or tightened to a desired tautness, the locking nuts must then be tightened again.
It can take several minutes to perform the above-described procedure. The locking nuts are very tight, and must be loosened and re-tightened with a socket wrench or other high torque tool. There are many times, such as when a firefighter is in the field and fighting a fast-moving fire, where a quick loosening or tightening of the chain is imperative. Conventional chain saws, however, are designed as described above and thus do not enable such quick adjustment.
In view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how a chain saw could be modified to enable quick loosening or tightening of the cutting element of the saw with respect to the elongate flat blade around which the cutting element extends.